Implantable biosensor platforms are complex miniaturized devices that are geared to monitor the concentration of metabolites and other biochemicals in their immediate vicinity. One example of such a biosensor device is an implantable glucose sensor that can assist in the proper management of diseases, such as diabetes mellitus. In general, such biosensor platforms consist of many components in addition to the actual biosensing element. Such components typically include electronic, optoelectronic, micro-electromechanical (MEM), ultrasound and radiofrequency (RF) devices, which are configured for powering, signal processing and wireless communication operations. In the presence of moisture and oxygen, these components are particularly sensitive to corrosion and therefore should be packaged in such a way that they are impervious to their environmental elements, such as gases and body fluids. On the other hand, current electrochemical sensing element (or elements) must be in direct contact with biological fluids in order to establish operable functionality. However, in the case of extreme miniaturization, such dual environmental requirements present major fabrication issues. To complicate matters, a variety of temperature and environmentally-sensitive biomolecules should be properly deposited on these sensors and coated with a number of semi-permeable membranes and/or drug containing entities to help regulate analyte diffusion, provide biocompatibility, suppress inflammation and prevent fibrosis.
Current device packaging can be divided into two parts: (A) sub-chip assembly and (B) device passivation. In terms of sub-chip assembly, chip to chip interconnects are typically formed using: (i) through-Si-vias (TSVs), (ii) flip-chip thermo-compression and thermosonic bonding, and (iii) wire bonding in either flat or wrap-around configurations. In terms of device passivation, techniques like (i) polymer encapsulation, (ii) thermo-compression molding, and (iii) sputtering or chemical vapor deposition (CVD) growth of a variety of insulating organic and inorganic materials have been employed. Unfortunately, these techniques fail to attain the required passivation needed for devices with the aforementioned dual environmental requirements, particularly when they reach extreme miniaturization and prolonged exposure to body fluids.
For example, referring to FIG. 1 a schematic block diagram of an IC chip 300 having device packaging in accordance with the prior art is illustrated and shows a variety of interconnects along with a through-Si-via (TSV) and flip-chip bonding of two individual IC wafers. In this case, two Si wafers (1) and (2) with their respective devices (3) and (4) are shown as being electrically connected via their interconnects (6) and (8), respectively, where the electrical connection is achieved through flip-chip bonding via a bonding layer (12). The interconnects (6) and (8) are shown as being isolated by host oxide layers (5). A TSV (10), which is isolated from the top wafer (2) by insulators (7) and (9), electrically connects the back side metal layer (11) to the top wafer interconnect layer (8). Such a conventional through-Si-via (TSV) requires the formation of a hole through the entire top wafer. This is undesirable because such holes, despite their metal filling, make this packaging prone to a variety of leakages should this wafer be exposed to a corrosive environment.